The present invention relates to a method of determining the degree of freshness of pieces of food such as fish, fillets of fish with or without skin, and other kinds of meat.
In evaluating the quality and the degree of freshness of meat and meat products, Including fish and fish products, it has up till now been necessary to make a more or less subjective evaluation based on the colour and the smell of the product. However, it would be desirable to be able to make a more objective evaluation or measurement of the degree of freshness.
During bacteriological decomposition of fish and other meat products various gases such as trimethylamine and other volatile bases are developed, and a "quality index" for fish based on a chemical determination of such developed gases has been proposed. Furthermore, the British patent specifications Nos. 1,262,749 and 1,287,190 disclose an apparatus for electrically determining the degree of freshness or the condition of food products or the bacteriological decomposition of such products. The development of this known apparatus is based on a study showning that the dielectrical characteristics of fish meat change in a regular manner with the time period which has lapsed after killing of the fish, when the meat is kept at a certain temperature. A report concerning this study which was made at "Torry Research Station", Aberdeen, and made by A. C. Jason and A. Lees, was published in the British "Department of Trade and Industry" in April, 1971.
This known apparatus is intended for measurement of randomly selected test samples, the apparatus comprising an abutment surface having electrical electrodes embedded therein. The freshness of a fish is measured by contacting the abutment surface of the apparatus with one side of the fish, and the result of the measurement may then be read from a digital display or another kind of display unit. Tests have shown that the measuring results obtained by means of this known apparatus are substantially independent of the position of which the measurement is carried out provided that the abutment surface of the apparatus is placed adjacent to the median line of the fish and not too close to the head or tail of the fish, it is therefore proposed to use the known apparatus for making a single measurement for each fish at a closely defined position adjacent to the median line of the fish.